- client: Clear input field when switching from logs page

Close #1523

Squashed commit of the following:

commit 9ae9b0e480c2ec6bd835faf4caccacd8c1fdfe9f
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri Jul 3 17:56:34 2020 +0300

    Setup babel and apply everywhere nullish coalescing and optional chaining operators

commit 0966063842a79078e1d61a54c271e18c9427b2b1
Merge: 42a54f2b 21dfb5ff
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri Jul 3 16:59:34 2020 +0300

    Merge branch 'master' into fix/1523

commit 42a54f2ba0d8f5f4e4c04f16abc507b5d9009035
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri Jul 3 13:30:25 2020 +0300

    Center mobile tooltip buttons

commit 9cdd501a863b596f1d903f8dd3c449ffbe4c1604
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri Jul 3 13:21:37 2020 +0300

    Add cross icon to clear input on click

commit 1308b93c42ffea2ffb7457c34aef96e5cdaccaf2
Merge: 265fec7c da546790
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Mon Jun 29 19:42:04 2020 +0300

    Merge branch 'master' of ssh://bit.adguard.com:7999/dns/adguard-home

commit 265fec7c72656b0c4738623cb470f1c14736230a
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Mon Jun 29 19:41:37 2020 +0300

    - client: Clear input field when switching from logs page

client/src/components/Settings/Dhcp/index.js

@@ -32,7 +32,7 @@ class Dhcp extends Component {
         const {
             config, check, processingDhcp, processingConfig,
         } = this.props.dhcp;
-        const otherDhcpFound = check && check.otherServer
+        const otherDhcpFound = check?.otherServer
             && check.otherServer.found === DHCP_STATUS_RESPONSE.YES;
         const filledConfig = Object.keys(config).every((key) => {
             if (key === 'enabled' || key === 'icmp_timeout_msec') {